High speed low temperature method for manufacturing and repairing semiconductor processing equipment and equipment produced using same

ABSTRACT

A method for the joining of ceramic pieces into an assembly adapted to be used in semiconductor processing. The joined pieces are adapted to withstand the environments within a process chamber during substrate processing, chamber cleaning processes, and the oxygenated atmosphere which may be seen within the shaft of a heater or electrostatic chuck. The ceramic pieces may be aluminum nitride and the pieces may be brazed with aluminum. The joint material is adapted to withstand both the environments within a process chamber during substrate processing, and the oxygenated atmosphere which may be seen within the shaft of a heater or electrostatic chuck. The joint is adapted to provide a hermetic seal across the joint. The joined pieces are adapted to be separated at a later time should rework or replacement of one of the pieces be desired.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/543,376 to Elliot et al., filed Nov. 17, 2014, which is acontinuation of U.S. patent application Ser. No. 13/543,727, filed Jul.6, 2012 to Elliot et al., now U.S. Pat. No. 8,932,690, issued Jan. 13,2015, which is hereby incorporated by reference in its entirety, whichclaimed priority to U.S. Provisional Application No. 61/565,396 filedNov. 30, 2011 to Elliot et al., which is hereby incorporated byreference in its entirety, and which claimed priority to U.S.Provisional Application No. 61/592,587 to Elliot et al., filed Jan. 30,2012, which is hereby incorporated by reference in its entirety, andwhich claimed priority to U.S. Provisional Application No. 61/605,707 toElliot et al., filed Mar. 1, 2012, which is hereby incorporated byreference in its entirety, and which claimed priority to U.S.Provisional Application No. 61/658,896 to Elliot et al., filed Jun. 12,2012, which is hereby incorporated by reference in its entirety.

BACKGROUND Field of the Invention

The present invention relates to a method for manufacturingsemiconductor processing equipment and equipment manufactured using suchmethods.

Description of Related Art

Semiconductor processing and similar manufacturing processes typicallyemploy thin film deposition techniques such as Chemical Vapor Deposition(CVD), Physical Vapor Deposition (PVD), Vapor Phase Epitaxy (VPE),Reactive Ion Etching, and other processing methods. In CVD processing,as well as in other manufacturing techniques, a substrate such as asilicon wafer is secured within a processing chamber using semiconductorprocessing equipment, such as a heater or an electrostatic chuck, andexposed to the particular processing conditions of the process. Theheater or electrostatic chuck is essentially a pedestal that, inaddition to securing the substrate, can in some instances also be usedto heat the substrate.

As heaters are exposed to high operating temperatures and corrosiveprocess gasses, and because good thermal conductivity is required forgood temperature control, prior art heaters have been made from a verylimited selection of materials, such as aluminum nitride (AlN) ceramicor PBN, silicon dioxide (quartz), graphite, and various metals such asaluminum alloys, nickel alloys, stainless steel alloys, Inconel, etc.Reactive process gasses which are typically used for semiconductorprocessing, or chamber cleaning, generally react with heaters made withmetal alloys. These reactions can produce corrosive by-products andother effects which can be detrimental to the desired process results.Ceramic materials can be much more resistant to reactions with typicalprocess gasses, and to corrosion from reaction by-products. However,ceramic materials can have limited methods of fabrication due toinherent material properties, and have high manufacturing costs.

The manufacture of semiconductor processing equipment using ceramics,such as heaters and electrostatic chucks with both a ceramic shaft and aceramic plate, currently involves hot pressing sub-components to partialdensity, and then again hot pressing an entire assembly until fulldensity is attained. In this type of manufacture, at least two drawbacksare seen. First, the hot pressing/sintering of a large, complex ceramicpiece requires a large physical space, and a multiplicity of sequentialsintering steps is required. Second, should a portion of the finishedpiece become damaged, or fail due to wear, there is no repair methodavailable to disassemble the large piece, likely leading to it beingscrapped. In the case of manufacture from two or more pieces which havealready been pressed to full density, there are also at least twodrawbacks. First, after the initial sintering of the major components,these components are typically joined using a liquid phase sinteringprocess to join the major components (in the case of aluminum nitride,for example), which requires high heat, high compressive force, and asignificant amount of time in a process oven capable of providing boththe high temperatures and the high compressive force. Often the highcompressive force applied to a shaft during this sintering to a plate,such as is done in the process of creating a ceramic heater, requiresthat the annular shaft walls be of thicker cross-sectional thicknessthan desired in the finished product in order to support thesecompressive forces. The shaft may then need to be machined down to afinal lesser thickness desired to keep heat flow down the shaft to aminimum. Second, should a portion of the finished piece become damaged,or fail due to wear, there is no repair method available to successfullydisassemble a large piece that has been joined in this fashion, likelyleading to it being scrapped.

An additional concern may be with regard to the repair of these piecesof semiconductor processing equipment, such as heater and electrostaticchucks with plate and shaft elements. Should a portion of a multi-pieceassembly of equipment be damaged, such as due to arcing, for example, itmay be desirable to dis-assemble the piece of equipment and re-useportions of it. These portions may retain significant financial value.With current methods of manufacturing, for example with regards toceramic heaters, there is no method available which would allow for therepair of equipment which would allow replacement of some portions andthe re-use of some portions of that equipment.

In order to reduce the cost and complexity of manufacturing a ceramicplate and shaft device, such as a heater, a joining method is neededwhich provides structural joining of the shaft to the plate, as well asa hermetic seal between the atmosphere seen within the shaft and theatmosphere outside of the device. This joint is an important aspect ofthe entire device, and may become critical in cases where the device issubjected to severe operating conditions such as high temperature, highpressure differences or highly oxidizing or reducing environments whichare tolerated by the sintered ceramic bodies themselves. To provide acommercially viable piece of semiconductor processing equipment thatuses a joint, the joint is required to maintain mechanical integrity,have compatibility with the sintered ceramic bodies, and retaingas-tightness even when subjected to the operating conditions.Accordingly an ideal joint would meet these requirements, especiallyduring thermal cycling.

It is therefore desired to provide a method of manufacturingsemiconductor processing equipment wherein a first sintered body isjoined to a second sintered body using a joining process which does nottake a significant amount of time, which does not require unduly hightemperatures, which is compatible with the process environmentchemistries, which results in a joint with a hermetic seal, and in whichthe joint may be disjoined to allow for repair of the equipment, andreuse of significant, and expensive, portions of it.

SUMMARY OF THE INVENTION

A method for the joining of ceramic pieces into an assembly adapted tobe used in semiconductor processing. The joined pieces are adapted towithstand the environments within a process chamber during substrateprocessing, chamber cleaning processes, and the oxygenated atmospherewhich may be seen within the shaft of a heater or electrostatic chuck.The ceramic pieces may be aluminum nitride and the pieces may be brazedwith aluminum. The joint material is adapted to withstand both theenvironments within a process chamber during substrate processing, andthe oxygenated atmosphere which may be seen within the shaft of a heateror electrostatic chuck. The joint is adapted to provide a hermetic sealacross the joint. The joined pieces are adapted to be separated at alater time should rework or replacement of one of the pieces be desired.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a plate and shaft device used in semiconductorprocessing according to some embodiments of the present invention.

FIG. 2 is a sketch of a high temperature press and oven for a plateaccording to some embodiments of the present invention.

FIG. 3 is a sketch of a high temperature press and oven for a pluralityof plates according to some embodiments of the present invention.

FIG. 4 is a sketch of a high temperature press and oven for a plate andshaft device according to some embodiments of the present invention.

FIG. 5A is a cross-sectional view of a joint between a plate and shaftaccording to some embodiments of the present invention.

FIG. 5B is a cross-sectional view of a joint between a plate and shaftaccording to some embodiments of the present invention.

FIG. 5C is a perspective view of a shaft end with mesas according tosome embodiments of the present invention.

FIG. 6 is a partial cross-sectional view of a plate and shaft device inuse in semiconductor manufacturing according to some embodiments of thepresent invention.

FIG. 7 is a close-up cross-sectional view of a joint between and shaftand a plate according to some embodiments of the present invention.

FIG. 8 is view of a plate and shaft device according to some embodimentsof the present invention.

FIG. 9 is an illustration of plate and shaft ready for assemblyaccording to some embodiments of the present invention.

FIG. 10 is an illustration of plate and shaft with fixturing ready forassembly according to some embodiments of the present invention.

FIG. 11 is an illustration of plate and shaft with fixturing ready forassembly according to some embodiments of the present invention.

FIG. 12 is an exploded view of a plate and shaft assembly with multipleconcentric joining layers according to some embodiments of the presentinvention.

DETAILED DESCRIPTION

In the processing of substrates, many processes require that thesubstrate be supported by semiconductor processing equipment components,such as a heater or an electro-static chuck. These components may bemaintained at, or required to operate in, vacuum conditions, hightemperatures, thermal cycling, corrosive atmospheres, and may be damagedduring their use during semiconductor manufacturing processes orotherwise. In some aspects, these components may be comprisedsubstantially or comprised fully of a ceramic such as aluminum nitride.The manufacture of these components from such a material has involvedcostly materials, and is time and equipment intensive, resulting in avery expensive end product.

Prior methods of manufacturing components such as heaters andelectrostatic chucks using ceramic materials have required process stepswith specialized atmospheres (such as vacuum, inert, or reducingatmospheres), very high temperatures, and very high contact pressures.The contact pressures may be applied using presses, and these pressesmay be adapted to operate inside a process chamber that provides thespecialized atmospheres, such as vacuum, and high temperatures. This mayrequire specialized presses and fixturing made of refractory materials,such as graphite, within the process chamber. The cost and complexity ofthese setups may be very high. In addition, the larger the componentthat is required to be pressed, the fewer components can be put intosuch a process oven. As the duration of the processes in the processovens with presses may be measured in days, and given the large expenseassociated with both the manufacture of and the running of the processovens/presses, a reduction in the number of steps which use theseprocess ovens which provide very high temperature, special atmospheres,and very high contact pressures during the manufacture of componentswill result in great savings.

FIG. 1 illustrates an exemplary plate and shaft device 100, such as aheater, used in semiconductor processing. In some aspects, the plate andshaft device 100 is composed of a ceramic, such as aluminum nitride.Other materials, such as alumina, silicon nitride, silicon carbide orberyllium oxide, may be used. In other aspects the plate may be aluminumnitride and the shaft may be zirconia, alumina, or other ceramic. Theheater has a shaft 101 which in turn supports a plate 102. The plate 102has a top surface 103. The shaft 101 may be a hollow cylinder. The plate102 may be a flat disc. Other subcomponents may be present. In somepresent processes, the plate 102 may be manufactured individually in aninitial process involving a process oven wherein the ceramic plate isformed. FIG. 2 conceptually illustrates a process oven 120 with a press121. The plate 122 may be compressed under temperature in a fixture 123adapted to be pressed by the press 121. The shaft 101 may also besimilarly manufactured in a process step. In a typical process, theplate and shaft are formed by loading of aluminum nitride powderincorporating a sintering aide such as yttria at about 4 weight % into amold, followed by compaction of the aluminum nitride powder into a“solid” state typically referred to as “green” ceramic, followed by ahigh-temperature liquid-phase sintering process which densities thealuminum nitride powder into a solid ceramic body. The high temperatureliquid-phase sintering process may see temperatures in the range of 1700C and contact pressures in the range of 2500 psi. The bodies are thenshaped into the required geometry by standard grinding techniques usingdiamond abrasives.

There are multiple functions of the shaft: one is to providevacuum-tight electrical communication through the wall of the vacuumchamber in order to apply electrical power to heater elements as well asa variety of other electrode types which may be embedded within theheater plate. Another is to allow temperature monitoring of the heaterplate using a monitoring device such as a thermocouple, and allowingthat thermocouple to reside outside of the processing chamber in orderto avoid interaction such as corrosion between the materials of thethermocouple and the process chemicals, as well as allowing thethermocouple junction to operate in a non-vacuum environment for rapidresponse. Another function is to provide isolation of the materials usedfor the previously mentioned electrical communication from theprocessing environment. Materials used for electrical communication aretypically metallic, which could thereby interact with process chemicalsused in the processing environment in ways which could be detrimental tothe processing results, and detrimental to the lifetime of the metallicmaterials used for electrical communication.

Given the relatively flat nature of the plate, a plurality of plates 142may be formed in a single process by stacking a plurality of platemolding fixtures 143 along the axial direction of the press 141 whichresides within the process oven 140, as seen conceptually in FIG. 3. Theshafts may also be formed in a similar process using the press in theprocess oven.

In the overall process of manufacturing a heater used in semiconductorprocessing both the step of forming plates and forming shafts requiresignificant commitments of time and energy. Given the cost of thespecialized high temperature ovens, and that the process steps offorming the plates and forming the shafts each may require the use of aspecialized process oven for days, a considerable investment of bothtime and money has been invested just to get the overall process to thepoint where the shaft and plate have been completed. Yet a further stepin the specialized process oven is required in present processes toaffix the plate to the shaft. An example of this step would be to jointhe shaft to the plate using a liquid phase sintering step in thespecialized high temperature process oven with a press. This third stepin the specialized process oven also requires significant space in sucha process oven as the assembled configuration of the heater includesboth the length of the shaft and the diameter of the plate. Although themanufacture of just the shafts may take a similar amount of axiallength, the diameter of the shafts is such that multiple shafts may beproduced in parallel in a single process.

As seen in FIG. 4, the joining process to sinter the shaft to the plateagain requires the use of a process oven 160 with a press 161. A set offixturing 164, 165 is used to position the plate 162 and the shaft 163,and to transmit the pressure delivered by the press 161.

Once the heater is completed, it may be used in semiconductorprocessing. The heater is likely to be used in harsh conditions,including corrosive gasses, high temperatures, thermal cycling, and gasplasmas. In addition, the heater may be subject to inadvertent impacts.Should the plate or the shaft become damaged, the opportunities forrepair of a plate and shaft device joined by liquid phase sintering arelimited, perhaps non-existent.

Another prior method for joining ceramic shafts to ceramic platesinvolves the bolting of the shaft to the plate. Such systems are nothermetic even where the adjoining surfaces are polished to enhance thequality of the seal. A constant positive purge gas pressure is requiredinto the inside of the shaft to reduce process gas infiltration.

An improved method for manufacturing semiconductor processing equipmentmay involve the joining of a shaft and a plate, which have beendescribed above, into a final joined assembly without the time consumingand expensive step of an additional liquid phase sintering with hightemperatures and high contact pressures. The shaft and plate may bejoined with a brazing method for joining ceramics. An example of abrazing method for joining together first and second ceramic objects mayinclude the steps of bringing the first and second objects together witha metal binder selected from the group consisting of aluminum and analuminum alloy disposed between the first and second ceramic objects,heating the metal binder to a temperature of at least 800 C in vacuum,and cooling the metal binder to a temperature below its melting point sothat the metal binder hardens and creates a hermetic seal so as to jointhe first member to the second member. Various geometries of brazejoints may be implemented according to methods described herein.

FIG. 5A shows a cross section of a first embodiment of a joint in whicha first ceramic object, which may be a ceramic shaft 181, for example,may be joined to a second ceramic object, which may be made of the sameor a different material, and which may be a ceramic plate 182, forexample. A braze filler material 180 may be included, which can beselected from the combinations of braze materials or binders describedherein and may be delivered to the joint according to the methodsdescribed herein. With respect to the joint depicted in FIG. 5A, theshaft 181 is positioned such that it abuts the plate, with only thebraze filler interposed between the surfaces to be joined, for exampleend surface 183 of the end 185 of the shaft 181 and an interface surface184 of the plate 182. The thickness of the joint is exaggerated forclarity of illustration.

FIG. 5B shows a cross section of a second embodiment of a joint in whicha first ceramic object, which may be a ceramic shaft 191, for example,may be joined to a second ceramic object, which may be made of the sameor a different material, and which may be a ceramic plate 192, forexample. A joining material, such as braze filler material 190, may beincluded, which can be selected from the combinations of braze materialsor binders described herein and may be delivered to the joint accordingto the methods described herein. With respect to the joint depicted inFIG. 5B, the shaft 191 is positioned such that it abuts the plate, withonly the braze filler interposed between the surfaces to be joined, forexample surface 193 of the shaft and surface 194 of the plate. Theinterface surface 194 of the plate 192 may reside in a recess 195 in theplate. The thickness of the joint is exaggerated for clarity ofillustration.

The embodiments as illustrated in FIGS. 5A and 5B may include aplurality of standoffs adapted to maintain a minimum braze layerthickness. In some embodiments, as seen in FIG. 5C, the shaft 191 mayutilize a plurality of mesas 171 on the end 172 of the shaft 191 whichis to be joined to the plate. The mesas 171 may be part of the samestructure as the shaft 191, and may be formed by machining awaystructure from the shaft, leaving the mesas. In some embodiments, themesas may be used to create a minimum braze layer thickness of theremainder of the shaft end 172 from the mating surface of the plate. Insome embodiments, the braze filler material, prior to brazing, will bethicker than the distance maintained by the mesas between the shaft endand the plate. With appropriate tolerance control on the interfacesurface of the plate and of the shaft and mesas, the tolerance controlof the finished plate and shaft device may be achieved as the mesas moveto contact the plate interface during the brazing step. In someembodiments, other methods may be used to establish a minimum brazelayer thickness. In some embodiments, ceramic spheres may be used toestablish a minimum braze layer thickness.

As seen in FIG. 6, the brazing material may bridge between two distinctatmospheres, both of which may present significant problems for priorbrazing materials. On an external surface 207 of the semiconductorprocessing equipment, such as a heater 205, the brazing material must becompatible with the processes occurring in, and the environment 201present in, the semiconductor processing chamber 200 in which the heater205 will be used. The heater 205 may have a substrate 206 affixed to atop surface of the plate 203, which is supported by a shaft 204. On aninternal surface 208 of the heater 205, the brazing material must becompatible with a different atmosphere 202, which may be an oxygenatedatmosphere. Prior brazing materials used with ceramics have not beenable to meet both of these criteria. For example, braze elementscontaining copper, silver, or gold may interfere with the latticestructure of the silicon wafer being processed, and are thus notappropriate. However, in the case of a brazed joint joining a heaterplate to a heater shaft, the interior of the shaft typically sees a hightemperature, and has an oxygenated atmosphere within the center of a thehollow shaft. The portion of the braze joint which would be exposed tothis atmosphere will oxidize, and may oxidize into the joint, resultingin a failure of the hermeticity of the joint. In addition to structuralattachment, the joint between the shaft and the plate of these devicesto be used in semiconductor manufacturing must be hermetic in many, ifnot most or all, uses.

A braze material which will be compatible with both of the atmospheresseen on both sides across a joint in such a device is aluminum. Aluminumhas a property of forming a self-limiting layer of oxidized aluminum.This layer is generally homogenous, and, once formed, prevents orsignificantly limits additional oxygen or other oxidizing chemistries(such as fluorine chemistries) penetrating to the base aluminum andcontinuing the oxidation process. In this way, there is an initial briefperiod of oxidation or corrosion of the aluminum, which is thensubstantially stopped or slowed by the oxide (or fluoride) layer whichhas been formed on the surface of the aluminum. The braze material, ormetal binder, may be in the form of a sheet, a powder, a thin film, orbe of any other form factor suitable for the brazing processes describedherein. For example, the metal binder may be a sheet having a thicknessranging from 0.005 millimeters to 0.300 millimeters. In one embodiment,the braze material may be a sheet in the form of an annular ring havinga thickness of approximately 0.006 inches. The mesas may have a mesastandoff height of 0.004 inches. In some embodiments, thicker brazelayers are used. Typically, alloying constituents (such as magnesium,for example) in aluminum are formed as precipitates in between the grainboundaries of the aluminum. While they can reduce the oxidationresistance of the aluminum bonding layer, typically these precipitatesdo not form contiguous pathways through the aluminum, and thereby do notallow penetration of the oxidizing agents through the full aluminumlayer, and thus leaving intact the self-limiting oxide-layercharacteristic of aluminum which provides its corrosion resistance. Inthe embodiments using an aluminum alloy which contains constituentswhich can form precipitates, process parameters, including coolingprotocols, would be adapted to minimize the precipitates in the grainboundary. For example, in one embodiment, the metal binder or filler maybe aluminum having a purity of at least 99.5%. In some embodiments, acommercially available aluminum foil, which may have a purity of greaterthan 89%, may be used. In some embodiments, alloys are used. Thesealloys may include Al-5 w % Zr, Al-5 w % Ti, commercial alloys #6061,#7005, #5083, and #7075. These alloys may be used with a joiningtemperature in the range of 1100 C-1200 C. These alloys may be used witha lower temperature in some embodiments.

FIG. 7 illustrates a joint 220 used to join a plate 215 to a shaft 214according to some embodiments of the present invention. The joint 220has created a structural and hermetic joint which structurally supportsthe attachment of the plate 215 to the shaft 214. The joint 220 hascreated a hermetic seal which isolates the shaft atmosphere 212 seen bythe interior surface 218 of the shaft 214 from the chamber atmosphere211 seen along the exterior surface 217 of the shaft 214 and within theprocess chamber. The joint 220 may be exposed to both the shaftatmosphere and the chamber atmosphere and must therefore be ablewithstand such exposure without degradation which may result in the lossof the hermetic seal. In this embodiment, the joint may be aluminum andthe plate and the shaft may be ceramic such as aluminum nitride. In someembodiments, the joint 220 may be of aluminum, and which substantiallyremains in the joint region after the joining process. The residualaluminum may allow for disjoining of the joint for repair, rework, orother reasons.

FIG. 8 shows one embodiment of a schematic illustration of a heatercolumn used in a semiconductor processing chamber. The heater 300, whichmay be a ceramic heater, can include a radio frequency antenna 310, aheater element 320, a shaft 330, a plate 340, and a mounting flange 350.One embodiment of a brazing method for joining together a shaft 330 anda plate 340, both or either one of which may be made of aluminumnitride, to form the heater 300 may be implemented as follows. In someembodiments, a poly-crystalline AlN is used, and is comprised of 96% AlNand 4% Yttria. Such a ceramic may be used in industrial applicationsbecause during the liquid phase sintering used to manufacture theceramic, a lower temperature may be used. The lower temperature process,in contrast to polycrystalline AlN without a sintering aide, reducesmanufacturing costs of the ceramic. The poly-crystalline AlN with addedYttria may also have preferred material properties, such a being lessbrittle. Yttria and other dopants are often used for manufacturabilityand tuning of material properties. With a poly-crystalline AlN such as96% AlN-4% Yttria ceramic, the ceramic presents grains of AlN which areinterspersed with yttrium aluminate. When this ceramic is presented withaluminum, such as joining layers according to some embodiments of thepresent invention, at higher temperature such as above the liquidustemperature of Al, the Al brazing material may react with the yttriumaluminate resulting in the dislodging and release of some of the AlNgrains at the surface of the ceramic. The AlN grains themselves do notreact with the aluminum joining layer, nor is diffusion of the aluminuminto the AlN grains seen. The non-susceptibility of AlN to diffusionwith aluminum under the conditions of processes according to embodimentsof the present invention results in the preservation of the materialproperties, and the material identity, of the ceramic after the brazingstep in the manufacturing of the plate and shaft assembly.

A sheet of aluminum or aluminum alloy metal binder or filler may beprovided between the shaft and the plate, and the shaft and the platemay be brought together with the sheet of the metal binder disposedtherebetween. The metal binder or filler may then be heated in a vacuumto a temperature of at least 800 C and cooled to a temperature below 600C so that the metal binder or filler hardens and creates a hermetic sealjoining the shaft to the plate. The shaft of said heater may be of solidmaterial or it may be hollow in conformation.

In an exemplary embodiment, the plate and shaft may both be of aluminumnitride and both have been separately formed previously using a liquidphase sintering process. The plate may be approximately 9-13 inches indiameter and 0.5 to 0.75 inches thick in some embodiments. The shaft maybe a hollow cylinder which is 5-10 inches long with a wall thickness of0.1 inches. As previously seen in FIG. 5A, the plate 182 may have arecess 185 adapted to receive an outer surface of a first end of theshaft 181. As previously seen in FIG. 5C, mesas may be present on theend of the shaft which abuts the plate. The mesas may be 0.004 incheshigh. The plate 182 and shaft 181 may be fixtured together for a joiningstep with a brazing material 180 of aluminum foil placed between thepieces along the end of the shaft and within the recess of the plate.The brazing material may be 0.006 inches thick prior to brazing with acompleted joint minimum thickness of 0.004 inches. The brazing materialmay be aluminum with 0.4 Wt. % Fe.

The fixturing may put a contact pressure of approximately 2-200 psi ontothe joint contact area. In some embodiments the contact pressure may bein the range of 2-40 psi. The contact pressure used at this step issignificantly lower than that seen in the joining step using hotpressing/sintering as seen in prior processes, which may use pressuresin the range of 2000-3000 psi. With the much lower contact pressures ofthe present methods, the specialized presses of the previous methods arenot needed. The pressures needed for the joining of the plate to theshaft using the present methods may be able to be provided using simplefixturing, which may include a mass placed onto the fixturing usinggravity to provide the contact pressure. In some embodiments, contactbetween the interface portion of the shaft and the brazing element, aswell as contact between the interface portion of the plate and thebrazing element, will provide contact pressure sufficient for joining.Thus, the fixture assembly need not be acted upon by a press separatefrom the fixture assembly itself. The fixtured assembly may then beplaced in a process oven. The oven may be evacuated to a pressure of1×10E−5 Torr. In some aspects, vacuum is applied to remove residualoxygen. In some embodiments, a vacuum of lower than 1×10E−4 Torr isused. In some embodiments, a vacuum of lower than 1×10E−5 Torr is used.Of note with regard to this step is that the high temperature oven withhigh contact pressure fixturing, which was required during themanufacture of the ceramic components (shaft and plate), is not neededfor this joining of the shaft and plate. Upon initiating the heatingcycle, the temperature may be raised slowly, for example 15 C per minuteto 200 C and then 20 C per minute thereafter, to standardizedtemperatures, for example, 600 C and the joining temperature, and heldat each temperature for a fixed dwell time to allow the vacuum torecover after heating, in order to minimize gradients and/or for otherreasons. When the braze temperature has been reached, the temperaturecan be held for a time to effect the braze reaction. In an exemplaryembodiment, the dwell temperature may be 800 C and the dwell time may be2 hours. In another exemplary embodiment, the dwell temperature may be1000 C and the dwell time may be 15 minutes. In another exemplaryembodiment, the dwell temperature may be 1150 and the dwell time may be30-45 minutes. In some embodiments, the dwell temperature does notexceed a maximum of 1200 C. In some embodiments, the dwell temperaturedoes not exceed a maximum of 1300 C. Upon achieving sufficient brazedwell time, the furnace may be cooled at a rate of 20 C per minute, orlower when the inherent furnace cooling rate is less, to roomtemperature. The furnace may be brought to atmospheric pressure, openedand the brazed assembly may be removed for inspection, characterizationand/or evaluation.

In some aspects, the brazing element is brought to a temperature abovethe melting (liquidus) temperature under a controlled atmosphere, whichmay be a vacuum. At the desired brazing temperature, the brazing elementthen flows over the substrate surfaces adjoining the filler material(wetting) and forming the basis of the desired joint. A vacuum ambienthelps insure that residual gas existing in the joint region is removedinsuring a more complete wetting of the joint surfaces includinginfusion of the liquid filler into any contours, pores, crevices, andreadily accessible intergranular spaces that may exist in the surfacesof the parts comprising the final joined item.

The wetting and flow of the brazing layer may be sensitive to a varietyof factors. The factors of concern include the braze materialcomposition, the ceramic composition, the composition of the ambientatmosphere during the joining process, which includes the level ofoxygen in the chamber during the joining process, the temperature, thetime at temperature, the thickness of the braze material, the surfacecharacteristics of the material to be joined, the geometry of the piecesto be joined, and the physical pressure applied across the joint duringthe joining process.

In some embodiments, the plate and shaft may comprise differentceramics. The plate may be adapted to provide a high conductive heatcoefficient, whereas the shaft may be adapted to provide a lowerconductive heat coefficient such that heat is not lost down the shafttowards the mounting appurtenances of the process chamber. For example,the plate may be made of aluminum nitride and the shaft may be made ofzirconia.

FIGS. 9-11 illustrate a joining process which may join a shaft to aplate according to some embodiments of the present invention. Thejoining process may be run in a process oven with lower temperatures,contact pressures, and lower time and cost commitments than in previousjoining operations.

In some embodiments, as seen in FIG. 9, alignment and location of theshaft and plate is maintained by part geometries, eliminating fixturingand post-bond machining. Weighting may be used to insure there is nomovement during bonding process, other than some axial movement as thebraze material melts. The plate 400 may be placed top down with ajoining element 402 within a recess 403 in the back surface of the plate400. The shaft 401 may be inserted vertically downward into the recess403 within the plate 400. A weight 404 may be placed on the shaft 401 toprovide some contact pressure during the joining process.

In some embodiments, as seen in FIG. 10, location of the shaft and plateis maintained by part geometries, reducing post-bond machining.Fixturing may be required to maintain perpendicularity between shaft andplate during bond processing. In some embodiments, the tolerancing ofthe mesas and the interface portion of the plate may be used to controlthe dimensions and tolerances of the final assembly. Weighting may alsobe used to insure there is no movement during bonding process, otherthan some axial movement as the braze material melts. The plate 410 maybe placed top down with a joining element 412 within a recess 413 in theback surface of the plate 410. The shaft 411 may be inserted verticallydownward into the recess 413 within the plate 410. A fixture 415 isadapted to support and locate the shaft 411. A weight 414 may be placedon the shaft 411 to provide some contact pressure during the joiningprocess. In some embodiments, a weight is not used. In some embodiments,the mass of the items to be joined may provide force, with gravity, toapply pressure between the items to be joined.

In some embodiments, as seen in FIG. 11, location and perpendicularityof shaft/plate is maintained by fixturing. Fixturing may not be precisedue to thermal expansion and machining tolerances—therefore, post-bondmachining may be required. The shaft diameter may be increased toaccommodate required material removal to meet final dimensionalrequirements. Again, weighting may be used to insure there is nomovement during bonding process, other than some axial movement as thebraze material melts. The plate 420 may be placed top down with ajoining element 422 above the back surface of the plate 420. The shaft421 may be placed onto the plate 420 to create a plate and shaftpre-assembly. A fixture 425 is adapted to support and locate the shaft421. The fixture 425 may be keyed to the plate to provide positionalintegrity. A weight 424 may be placed on the shaft 411 to provide somecontact pressure during the joining process.

An aspect of the current invention is the maximum operating temperatureof the bonded shaft-plate as defined by the decreasing tensile strength,with temperature, of the aluminum or aluminum alloy selected for thejoining. For example, if pure aluminum is employed as the joiningmaterial, the structural strength of the bond between the shaft andplate becomes quite low as the temperature of the joint approaches themelting temperature of the aluminum, generally considered to be 660 C.In practice, when using 99.5% or purer aluminum, the shaft-plateassembly will withstand all normal and expected stresses encountered ina typical wafer processing tool to a temperature of 600 C. However, somesemiconductor device fabrication processes require temperatures greaterthan 600 C.

A further embodiment of the present invention is seen in FIG. 12. As hasbeen disclosed, aluminum or aluminum alloy material, 400, may be used tojoin the shaft 404 to the plate 405 in a hermetic fashion. Further,another joining material 401 that has both the ability to bond with AlNand a higher melting temperature than aluminum, that is, greater than660 C, may be used as a structural bond to extend the usable temperatureof the shaft-plate assembly to higher temperatures. For example, atitanium-nickel alloy has been demonstrated to bond to aluminum nitrideat a temperature within the bonding temperature range used for aluminumas previously described. Other titanium and zirconium alloys may be usedas well, many of them containing silver, copper, or gold as alloyingelements. Because of their higher melting temperatures, the use of thesealloys extends the usable temperature range of the shaft-plate assemblyto 700 C or 800 C or 900 C. However, as previously discussed, theelements silver, copper, and gold may be detrimental to the crystallinestructure of wafers and must be isolated from the process environmentwith extreme care. In a similar fashion, titanium and zirconium areeasily and detrimentally oxidized when exposed to air at temperaturestypically used in wafer process. A solution is to use aluminum “guardbands” around the structural joining material, one band disposed to theprocess side if necessary to prevent the migration of detrimentalelements to the wafer, and one band disposed to the atmosphere side toprevent oxidation of the titanium or zirconium structural bond. In someembodiments, there may be a guard band on only the inner or only theouter side of the joint of other material. In some embodiments, theconcentric joints may be at different elevations, in that the end of theshaft has a plurality of plateaus wherein the joints are placed.

As seen in FIG. 12, a flange 403 is hermetically sealed, usually with anelastomeric O-ring, to the process chamber base (not shown). Electricalconnections for heating or electrostatic chucking or RF conduction arerouted through the shaft center 407 and connect to the plate in thecentral area 406. Typically the electrical connections and shaft centerare in an ambient (air) environment.

After the step of joining the plate to the shaft, the shaft and/or theplate may undergo further machining in the completion of the finishedpiece. The pressures required to achieve the liquid-phase sinteringnecessary for typical previous plate-shaft joining required mechanicalstrengths higher than those provided by typical finish dimensions ofheater shafts, as the components needed to withstand the high forcesassociated with the high pressures of the previous joining process.Therefore, to reduce cracking failures during the bonding process,thicker ceramic sections may have been used for the shaft than areneeded in the final configuration. Final required dimensions are thenachieved by grinding the bonded plate/shaft assembly after bonding.Although the plate and shaft assemblies of the present invention mayundergo some further machining after joining in some embodiments, inother embodiments this is not required. The elimination of the need toutilize thick shafts to withstand forces of high contact pressurejoining of shafts and plates, as was required is past methods, removesanother time consuming and costly process step from the manufacture ofplate and shaft assemblies in processes according to embodiments of thepresent invention.

Another advantage of the joining method as described herein is thatjoints made according to some embodiments of the present invention mayallow for the disassembly of components, such as the shaft and theplate, if desired, to repair or replace one of those two components. Forexample, should a plate become damaged due to arc discharge, the platemay be removed from the assembly and replaced. This will allow the costsavings associated with the re-use of a shaft, for example. Also, withan inventory of shafts and plates on hand, a replacement heater may beassembled without need for a high temperature, high pressure process, asthe replacement component and the previously used component may bejoined according to embodiments of the present invention. Similarly,should the joint, which is both structural and hermetic, lose itshermeticity, the joint may be repaired.

A repair procedure for the unjoining of an assembly which has beenjoined according to embodiments of the present invention may proceed asfollows. The assembly may be placed in a process oven using a fixtureadapted to provide a tensile force across the joint. The fixturing mayput a tensile stress of approximately 2-30 psi onto the joint contactarea. The fixtured assembly may then be placed in a process oven. Theoven may be evacuated, although it may not be required during thesesteps. The temperature may be raised slowly, for example 15 C per minuteto 200 C and then 20 C per minute thereafter, to standardizedtemperatures, for example 400 C, and then to a disjoining temperature.Upon reaching the disjoining temperature, the pieces may come apart fromeach other. The disjoining temperature may be specific to the materialused in the brazing layer. The disjoining temperature may be in therange of 600-800 C in some embodiments. The disjoining temperature maybe in the range of 800-1000 C in some embodiments. The fixturing may beadapted to allow for a limited amount of motion between the two piecessuch that pieces are not damaged upon separation. The disjoiningtemperature may be material specific. The disjoining temperature may bein the range of 450 C to 660 C for aluminum.

Prior to the re-use of a previously used piece, such as a ceramic shaft,the piece may be prepared for re-use by machining the joint area suchthat irregular surfaces are removed. In some embodiments, it may bedesired that all of the residual brazing material be removed such thatthe total amount of brazing material in the joint is controlled when thepiece is joined to a new mating part.

In contrast to joining methods which create diffusion layers within theceramic, joining processes according to some embodiments of the presentinvention do not result in such a diffusion layer. Thus, the ceramic andthe brazing material retain the same material properties after thebrazing step that they had prior to the brazing step. Thus, should apiece be desired to be re-used after disjoining, the same material andthe same material properties will be present in the piece, allowing forre-use with known composition and properties.

It is appreciated that other components for use in a vacuum chamber maybe joined or repaired according to the methods described herein orcontemplated hereby, including the specific method described above.Although the processes described above have been primarily with regardto ceramic heaters, it should be understood that other equipment, suchas electrostatic chucks, vacuum chucks, and others, may also bemanufactured using processes according to embodiments of the presentinvention.

As evident from the above description, a wide variety of embodiments maybe configured from the description given herein and additionaladvantages and modifications will readily occur to those skilled in theart. The invention in its broader aspects is, therefore, not limited tothe specific details and illustrative examples shown and described.Accordingly, departures from such details may be made without departingfrom the spirit or scope of the applicant's general invention.

What is claimed is:
 1. A plate and shaft device used in semiconductorprocessing, said plate and shaft device comprising: a plate, said platecomprising a first ceramic, said plate comprising a joining interfacesurface of said first ceramic; a shaft, said shaft comprising a secondceramic, said shaft comprising an interior space and an exterior, saidshaft comprising a joining interface surface of said second ceramic,said shaft coupled to a bottom surface of said plate; a first metaljoining layer directly disposed between said joining interface surfaceof said plate and said joining interface surface of said shaft, whereinsaid first metal joining layer hermetically seals said interior space ofsaid shaft from said exterior of said shaft through said first metaljoining layer, said first metal joining layer comprising aluminum,wherein the conductive heat coefficient of said first ceramic is higherthan the conductive heat coefficient of said second ceramic.
 2. Theplate and shaft device of claim 1 wherein said first ceramic comprisesaluminum nitride and said second ceramic comprises zirconia.
 3. Theplate and shaft device of claim 1 wherein said first metal joining layercomprises greater than 89% by weight aluminum.
 4. The plate and shaftdevice of claim 1 wherein said first metal joining layer comprisesgreater than 89% by weight aluminum.
 5. The plate and shaft device ofclaim 2 wherein said first metal joining layer comprises greater than99% by weight aluminum.
 6. The plate and shaft device of claim 2 whereinsaid first metal joining layer comprises greater than 99% by weightaluminum.
 7. A plate and shaft device used in semiconductor processing,said plate and shaft device comprising: a plate, said plate comprisingaluminum nitride, said plate comprising a joining interface surface ofaluminum nitride; a shaft, said shaft comprising aluminum nitride, saidshaft comprising an interior space and an exterior, said shaftcomprising a joining interface surface of aluminum nitride, said shaftcoupled to a bottom surface of said plate; a first metal joining layerdirectly disposed between said joining interface surface of said plateand said joining interface surface of said shaft, wherein said firstmetal joining layer hermetically seals said interior space of said shaftfrom said exterior of said shaft through said first metal joining layer,said first metal joining layer comprising aluminum, wherein said firstmetal joining layer comprises greater than 99% by weight aluminum.